I have received one PIP in my entire career - it was at an employer which was recently purchased by another company, shortly after the majority of my team was replaced with offshore contractors.

I was not at all surprised at receiving it, despite my performance being roughly on par with my entire tenure in that position up to that point. If anything, I was happy to receive it as it prompted me to start interviewing elsewhere earlier.

Several cases like this on here. These would be valid wrongful termination lawsuits.